arm: dts: k3-am642-evm-u-boot: Add u-boot, dm-spl tag in the pinmux node of mmc1

Add u-boot,dm-spl tag in the pinmux device tree node, required for MMCSD1
subsystem.

Fixes: b6059ddc45b9 ("arm: dts: k3-am642: Add r5 specific dt support")
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
diff --git a/arch/arm/dts/k3-am642-evm-u-boot.dtsi b/arch/arm/dts/k3-am642-evm-u-boot.dtsi
index ed38b72..03688a5 100644
--- a/arch/arm/dts/k3-am642-evm-u-boot.dtsi
+++ b/arch/arm/dts/k3-am642-evm-u-boot.dtsi
@@ -59,6 +59,10 @@
 	u-boot,dm-spl;
 };
 
+&main_mmc1_pins_default {
+	u-boot,dm-spl;
+};
+
 &main_usb0_pins_default {
 	u-boot,dm-spl;
 };